Our efforts over the past year have been aimed at defining the differentiated and growth properties of the distal tubular kidney epithelial cell line, MDCK. We plan to continue to concentrate our effort on these two problems. We are characterizing two Na ions transport systems in these cells: one is a H ions/Na ions antiport system which is inhibited by amiloride and is energy independent; the other is an Na/K ions cotransport system which is furosemide inhibited and appears to be ATP dependent. We are also attempting to ascertain the roles of cAMP, Na ions transport and rates of nutrient transport in the regulation of cell growth.